The present invention relates to pressure gauges in which the sensitive element comprises a thin wafer of piezoelectric material. The wafer is elastically deformed as a result of the pressures exerted on its faces. To obtain an electrical measuring signal whose frequency is proportional to the differential pressure exerted on the deformable wafer four sets of interdigitated comb shaped transducers are deposited on one of its faces so as to form two elastic surface wave delay lines. By looping two amplifiers by means of these delay lines two oscillators are obtained, whose oscillating frequencies are sensitive to the deformations undergone by the wafer. The signals supplied by the oscillators are applied to a mixer stage, which provides a measuring signal, whose frequency is equal to the difference between the incident signals. This measuring procedure uses oscillating frequencies of several tens megahertz, but the frequency showing the differential pressure is considerably lower. As a result it is very difficult to construct such a gauge because it is necessary to operate two oscillators having frequencies which are very close to one another without them pulling in.
The construction is made all the more difficult by the fact that it is necessary to ensure a good manufacturing reproducibility and in no way excessive manufacturing costs. The dimensions of the components of the gauge have been reduced to reduce manufacturing costs. However, this miniaturization imposes a very careful choice of the mechanical and electrical assembly modes, because these modes directly influence the satisfactory operation of the products and their rational manufacture.